_spfb.themailspec.com has no CNAME records.
Question and response
Question
dig _spfb.themailspec.com. NS
Answer
The response has no answer records.
Authority
themailspec.com. 3529 SOA pns1.cloud.sg. dnsadmin.cloud.sg. 2026022806 7200 1800 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0